1. Field of the Invention
The present invention relates to a sound coder/decoder circuit and a mobile communication device using same.
2. Description of the Related Art
To meet a demand for driving a battery for long hours, a mobile communication device, particularly a mobile telephone must operate with a further lower power consumption.
FIG. 7 shows a schematic structure of a conventional mobile communication device.
A sound inputted to a microphone 10 is converted into an electric signal and provided to an audio interface 11. The audio interface 11 amplifies the signal, digitizes the signal with sampling it, and provides the signal as sound data PCM1 to a sound coder/decoder circuit (CODEC) 12. The circuit 12 encodes the sound data PCM1 in order to reduce a data volume and correct an error, and provides the same as encoded data TCH1 to a frame assemble/disassemble circuit 13. The circuit 13 multiplexes control data over the encoded data TCH1 so that the data are formed into frames, and performs time compression of the frames and provides the frames to a modem 14 at a rate of one frame/20 ms, for instance. A processing at the frame assemble/disassemble circuit 13 is TDMA (time division multiple access) or CDMA (code division multiple access). The multiplex data are modulated at the modem 14, amplified and converted into an electric wave at an RF circuit 15, and transmitted from an antenna 16.
A signal received through the antenna 16 at the RF circuit 15 is selected as to a frequency by a band pass filter and amplified, demodulated at the modem 14, separated at the frame assemble/disassemble circuit 13 into control data and encoded data TCH2, and the encoded data TCH2 are provided to the sound coder/decoder circuit 12. The circuit 12 decodes the data TCH2 to convert into sound data PCM2, and provides the sound data PCM2 to the audio interface 11. The audio interface 11 converts the sound data PCM2 into an analog signal, and provides it through a low pass filter and an amplifier to a speaker 17.
If the sound data PCM1 from the audio interface 11 are silent data, it is not necessary for the sound coder/decoder circuit 12 to convert the sound data PCM1 into the encoded data TCH1. If silent PCM1 are converted, a wasteful consumption of electric power results.